The role of large arteries in controlling blood flow to the hand during severe local cooling.

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Abstract

Cold vasodilatation describes the increase in blood flow that follows initial vaso constriction when an extremity is exposed to an environment colder than 12'C. It
appears to be due mainly to cold paralysis of local resistance vessels. The reaction is very
variable between individuals who are generally chilled; this study was designed to show
whether constriction of large arteries of the forearm, protected by fat from local cooling,
is responsible for this, enabling such people to maintain low flow and heat loss during
cold stress.
Twelve subjects were exposed for 120 minutes to warm (38'C), control (24'C) or cold
(I 2'C) moving air. During the last half hour the non-dominant hand was cooled in ice
water. Arterial diameter and blood velocity in the brachial and radial arteries were
measured by ultrasound, and in 6 experiments pressure in both arteries was measured by
indwelling cannulae.
The arterial diameters constricted significantly in the cold, but only by 27% compared
to warm and 17% compared to control (radial), and by 19% compared to warm and 11 %
compared to control (brachial). Calculated pressure drop (mean ± S. E. ) between brachial
and radial arteries fell from 3.78 ± 0.23 mm Hg in the warm to 2.02 ± 0.15 mm Hg in
the cold. During hand immersion in ice water with increased flow, this pressure
difference rose in each of 5 cold subjects but never to more than 4.81 mm. Hg. Indwelling
arterial cannulae never showed a difference greater than 7.7 mm Hg between brachial
and radial arteries in any subject at any time. The general conclusion is that forearm
arteries exerted little control over hand blood flow in these circumstances, and that the
ability of some people to maintain low blood flow in very cold extremities is due to the
ability of downstream vessels to maintain constriction near O degrees C.